1. Field of the Invention
The present invention relates to solid polymer sorbents, and in particular to a solid polymer sorbent and the method of producing it used for fission molybdenum-99 (Mo-99) extraction from an irradiated uranyl sulfate solution.
2. Description of the Prior Art
At the present time more than 50% of the world's annual production of radionuclides are used for medical purposes, such as for the early diagnoses of diseases and for therapy. A basic condition of the use of radionuclides in medicine is the requirement that the radiation exposure of a patient be minimal. This necessitates the use of short-lived radionuclides. A nuclide with a short half-life, however, creates difficulties in transportation and storage. The preferred radionuclide for medical purposes is Mo-99 with a half-life of 66 hours. Mo-99 decay results in Tc-99m with a half-life of 6 hours, and about 140 keV of gamma (.gamma.) energy convenient for detection. Currently, more than 70% of diagnostic examinations are performed using this radionuclide.
Various means are used to produce the medical isotope Mo-99. These generally involve nuclear reactors with the final process being the chemical extraction of Mo-99. For example, U.S. Pat. No. 3,799,883 discloses dissolving uranium material in aqueous inorganic acid and then precipitating Mo-99 using alpha-benzoinoxime.
U.S. Pat. No. 5,596,611 discloses a small, dedicated uranyl nitrate homogeneous reactor for the production of Mo-99. A portion of the uranyl nitrate solution from the reactor is directly siphoned off and passed through columns of alumina to fix some of the fission products, including Mo-99, to the alumina. The fixed fission products from the alumina column are then removed through elution with a hydroxide and the Mo-99 is precipitated out of the resultant elutriant with alpha-benzoinoxime (.alpha.-BO).
A particular feature of .alpha.-BO is that Ag, Pb, Hg, Bi, Cu, Cd, As, Sb, Sn, Al, Fe, Ti, Zr, Cr(III), V(IV), Ce, U, Ni, Co, Mg, and Zn are not precipitated by it from sulfuric acid and Se, Te, Ru, Ro, Os, Ir, and Pt are not precipitated when they are alone in the solution.
The difficulty with .alpha.-BO Mo-99 complex extraction is the low absorption rate and the low radiation resistance on exposure to neutrons, .alpha.-, .beta.-, and .gamma.-rays of this sorbent.